Arc extinguishing structure



Feb 18, 1947.,

Filed Nov. 6, 1945 WITNESSES:

INVENTORS De/ber? 57/13 and ATTORNEY Patented Feb. 18, 1947 ARC EXTHIGUISHING STRUCTURE Delbert Ellis and Owen L. Taylor, Wilkinsburg,

Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa.. a corporation of Pennsylvania Application November 6, 1943, Serial No. 509,260

1 Claim. 1

Our invention relates to are extinguishing structures for alternating-current circuit breakers and the like contactors and, more particularly, to an arc deionizing structure of the type generally known from U. S. Patent No. 1,932,090, issued October 24, 1933, to Joseph Slepian.

Structures of this type contain a plurality of conductive plates which are spaced from each other along the path of a movable contact. Each of the plates has a V-shaped notch in alignment with the V-notch of the other plates, so that a groove is formed into which the arc is forced by the magnetic effect of the arc current and due to the magnetic action of a suitably located iron plate.

It is an object of our invention to improve the arc quenching effect of deionizing plate arrangements of the above-mentioned type so as to permit a considerable reduction in dimensions of the are extinguishing unit.

Another object of the invention is to intensify the efiect of such an arrangement to such an extent as to afiord a safe interruption of an are even without the use of an iron plate or the like magnetizable member around the arcing chamber. 1

We have discovered that these objects and advantages are achieved if the metal plates of the arc quenching structure are shaped and arranged so that they straddle the path of the movable contact surface and offer the are a foot point laterally of the movable member as well as near the periphery or front of the contact motion. This effect is obtained by providing a. substantially M-shaped notch in each plate and arranging the plate so that the contact passes between the legs of the M configuration and sufiiciently close to the legs and the central portion to permit the arc to strike laterally and frontally between the movable contact and the plate. We have been able in this manner to provide an arcing device of considerably reduced dimensions than those heretofore necessary for breakers of comparable rating. The increase in efficiency or reduction in space and material is especially noticeable in multi-pole switches with several arc chambers in a row.

According to another feature of the invention, the notched metal plates of the arc extinguishing structure are fully enclosed, preferably by insulating material, and have an opening near their edges away from the movable contact so that the interstices between the plates communicate with each other through the openings, one or several escape openings being provided in the enclosure (Cl. zoo- 144) of the plates to establish a connection between the interstices and the ambient atmosphere. This constitutes also to obtaining a satisfactory appertaining movable contact of the circuit breaker; and in Fi 4 a perspective view of the multi-pole arcing chamber of the circuit breaker partly broken away and partly dismantled.

Referring to Fig. 1, the numeral I denotes the movable contact arm of the circuit breaker. A saddle 2 is firmly mounted on the end of arm I and carries a contact bridge 3 which is provided with two contacts 4 and 5. A coiled compression spring 6 is arranged between the arm I and the bridge 3 and biases the bridge away from the arm.

The contact 4 carried by the brid e 3 cooperates with a stationary contact 1 which is connected with a terminal 8 and firmly mounted on the insulating base structure 9 'of the circuit breaker. Another stationary contact I0 for cooperation with the movable contact 5 is provided with a terminal I l and also firmly attached to the insulating base 9.

Fig. 1 shows the just mentioned contact ele-.

ments in the circuit interrupting position. For closing the circuit between terminals 8 and II, the arm I is moved clockwise so that contacts 4 and 5 engage contacts 1 and I0, respectively,.under contactpressure supplied by the spring 6. When opening the switch under current by turning the arm I l counterclockwise, two arcs will be drawn between contacts 4 and 1 and contacts 5 and I0, respectively. It is the purpose of the arc extinguishing structure described hereinafter to quench the arc occurring between contacts 5 and I 0, a separate arc quenching means being provided for extinguishing the are between contacts 4 and 1.

An insulating structure l4 so shaped as to enclose the interrupting and arcing space of the contacts is firmly mounted on the insulating base 9 of the circuit breaker. A plurality of conductive plates [5 consisting, for instance, of iron are arranged in an opening of the insulating enclosure l4 so as to extend in parallel and spaced relation to one another. Each of these metal plates. with the exception of an end plate denotedby I5 and serving to protect the adjacent surface of the insulating body I4, is shaped as apparent from Figs. 2 and 3. Each plate I5 has a recess substantially of M-shape. The center portion I6 of the plate is curved towards the path of the movable contact 5 and approaches this path so closely that an arc may strike between the points A and B indicated in Fig. 3. The two legs I! and [8 of the M-shaped plate have their inner edge curved away from the path of the movable contact and extend from the center portion I6 towards the path of contact motion and also beyond the periphery of this path, so as to oil'er the possibility that an arc may strike between the points C and D, or E and F indicated in Fig. 3, or between points similarly located at the lateral sides of the movable contact and the adjacent inner edge of the respective legs I1 and I8. The recess of each plate I5 is so shaped that two notches I9 and 20 are formed between the legs l1, l8 and the central portion I6 which recede from the path of contact movement.

The plates I5 and I5 are secured in the insulating enclosure I4 in the following manner. As

apparent from Fig. 4, the enclosure I4 has an opening, such as the one denoted by 24, tor the reception of each set of plates. The two opposite walls 25 of each opening 24 which extend substantially, in parallel to the plane of contact movement are rack-shaped, Thus a plurality of parallel grooves are formed for slidably engaging the outer edges of the legs I1 and I8 of each plate I5, so that the plates are rigidly heldv in place and prevented from vibrating and wearing the moulded enclosure. Each opening 24 is covered by an insulating cover plate 21 which is attached to the enclosure I4 by means of screws 28. The cover plate 21 lies adjacent to the top edge of each plate l5 opposite the contact path. It consists preferably of fibrous insulating material to assist in the extinction of arcs. The mitered or bevelled corners of the grid plates serve primarily to facilitate cementing the plates in place and provide also a better creepage between phases during arcing. The insulating enclosure I4 and cover plate 21 surround the plates I5 on the three sides not occupied by the switch contacts, and thus enclose the interstices between the plates I5 on these three sides. Each plate I5 is provided with a marginal indentation 2I which, in assembled condition, borders the plate 21, as best apparent from Fig. 2. In this manner, a communication is established between the interstices near the edge of the plates I5 remote from the contacts. The plate 21 has an escape opening 29 which connects the interstices with the ambient atmosphere. Due to the last-mentioned features, the arcing fire which may occur between the plates, especially at high-current intensities, is prevented from reaching the outside of the insulating enclosure while the ducts formed by the openings 2| and 29 permit the facilities an equalization of pressure.

When in operation, the are drawn between the separating contacts 5 and I is forced through its magnetic field to blow against the plate arrangement and is divided into a number of series connected partial arcs, each extending in the interstices between two adiacent plates. As explained in connection with Fig. 3, the initial location of the arc between the movable contact and the adjacent plate I may occur at the peripheral end or front of the contact as well as on the two lateral sides of the contact. The magnetic field efl'ective in the arcing space drives the loot point of any such arc away from its initial location and towards the apex of the notch I9 or 20, the initial location of the arc point and its direction of travel being dependent on the instantaneous direction of the alternating current to be interrupted. Due to the just mentioned displacement of the partial arcs along the inner edges of the central portion I6 and legs I1 and I8, the resistance of the total interrupting gas is increased and each partial are effectively cooled. As a result, the structure has the tendency to extinguish the partial arcs and to deionize the arc space to such an extent as to prevent a reignition when the current passes through one of the subsequent zero values. In this respect, the basic function of the plate arrangement is similar to that described in the above-mentioned patent to Slepian. However, due to the fact that the legs of the plates I5 extend laterally of the movable contact, and together with the curved central portion oi the recessed plates offer a plurality of possible initial arcing paths, the quenching efiect is considerably increased and hence permits the use of a smaller extinguishing structure for a given switch rating and the omission of the magnetizable backing plate-otherwise necessary. While such a reduction in dimensions may have the tendency of permitting the arcing fire to appear at the outside of the assembly, the above-described provision of an insulating enclosure and of ducts for establishing a communication of the interstitial spaces with the exterior elements suppress this tendency to a suflicient extent to permit taking full advantage of the increased enlciency of the extinguishing means. The saving in material and space thus afforded is especially noticeable in the case of multi-pole switches. Thus, according to Fig. 4, the interrupting contacts of such switches may be arranged close to one another within a single insulating enclosure I4. This leads to considerably reduced overall dimensions of such a multi-pole breaker.

Reverting to Fig. l of the drawing, it will be seen that in the illustrated embodiment a difierent arc quenching device is employed adjacent to contacts 4 and I. This device includes a substantially U-shaped strip I 2 of magnetizable material, such as iron, which is fastened at I3 to the insulating body I4. The two limbs of the U shaped strip are bent towards the interior of the base of the strip so as to form returning ends at 22 and 23. Upon separation of contact members 4 and I. an arc will be drawn between the contacts 4 and 1. The current flowing in the are forms a current loop which has its highest curvature and hence its strongest magnetic field at the center of the loop between the contacts. Therefore, the are between the contacts will move outwardly toward the U-shaped member I2. As such are lengthens, the current will follow the path of least resistance, and an arc will strike from each of the contacts 4 and I to therespective ends of the arms 22 and 23 substantially at the points closest to the contacts. In this manner, the are originally drawn between the contacts 4 and I is divided into two separate portions. At this time, the current will flow from contact 4 through one of the divided arc portions to arm 22 and thence through member I2 to the arm 23 and through the other are portion to the contact I.

Due to the shape of the U-shaped bends at 22 and 23, the direction in which the current flows through the outer path of the bends is reversed and a current loop is formed in member I2 which will have its strongest magnetic held in the bight of the loops. Such field will function to move the end of the are remote from the contact members 4 and l downwardly along the surface of the inwardly extending end of the arm 22 or 23. As a result, the resistance of the two separate arc portions will increase due to are lengthening. In this manner, the extinction of the arc at one of the subsequent zero passages of the alternating current is facilitated.

The just mentioned extinguishing structure adjacent to contacts 4 and 1, is more fully described in the copending application Serial No. 453,058, filed July 31, 1942, by Delbert Ellis and Owen L. Taylor, on Arc limiting devices, now Patent No. 2,356,039, and does not form an essential feature of the invention proper of the present application. It will be understood that in the case of double-break interrupters, the extinguishing means provided near the second pair of contacts may also consist of a plate arrangement as described previously in this specification, and it will also be obvious that a similar plate arrangement can be applied to single-break interrupters so that a second extinguishing device is superfluous.

Since numerous changes may be made in the above-described construction and different embodiments may be designed on the basis of this disclosure without departing from the spirit and scope of the invention, it is intended that the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

An electric current-interrupting device comprising a stationary contact, a, contact engageable with said stationary contact and movable away from said stationary contact along a given path, an arc extinguishing structure comprising a plurality of conductive plates arranged one above the other in spaced relationship, each of said plates having a central portion and two legs forming together a generally M-shaped recess, said central portion having a continuously rounded edge curved toward said path so as to have a midpoint located closest to said path in order to form a foot point for arcs to strike between said movable contact and said plate, said legs extending away from said central portion a suihcient extent to straddle said path and having respective inner edges continuously curved outwardly from said central portion so as to approach said path at the respective middle sections of said latter edges in order to form two respective additional foot points for arcs to strike between said movable contact and said plate, said curved edges of said central portion and said curved edges of said legs forming at their Juncture points two respective notches which recede from said path to cause lengthening of said arcs as they are magnetically forced toward said notches during the operation of the device.

DELBERT ELLIS. OWEN L. TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,080,611 Johnson May 18, 1937 1,868,442 Corbett July 19, 1932 2,147,430 Ellis et al. Feb. 14, 1939 

